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    <script>
        //演示的是数据类型
        //undefined
        // var a;
        // console.log(a)

        //2.null//object
        // var a = null;
        // console.log(typeof(a))
        // console.log(typeof a)

        // //3.number
        // var a = 123.123;
        // console.log(typeof a)

        //4.布尔//boolean
        // var a = true;
        // console.log(typeof a)

        //5.string
        var a = 'hellojs'
        console.log(typeof a)
    </script>
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